1. Field of the Invention
The present invention relates to a display apparatus including an organic electroluminescence (EL) device, and more particularly, to a full-color display apparatus in which one pixel includes multiple subpixels having different emission colors.
2. Description of the Related Art
In recent years, organic light-emitting devices that emit light spontaneously with a low drive voltage of about several volts are drawing attention. The organic electroluminescence (EL) device utilizes its excellent features such as surface emitting characteristics, light weight, and visibility and is being put into practical use as a light-emitting apparatus of a thin display, a lighting equipment, a head-mounted display, or a light source for a printhead of an electrophotographic printer.
The organic EL device has structure in which an emission layer made of an organic material and multiple layers made of organic materials having separated functions are sandwiched between an anode and a cathode, and an electrode on at least one light exit side is transparent. Due to this stack structure, light traveling in a direction at a critical angle or larger in each interface determined by a refractive index of the emission layer, a medium on the light exit side, and a refractive index of air into which light is finally released is totally reflected to be confined as propagating light in the device. The propagating light is absorbed by organic compound layers and metal electrodes in the device and is not extracted out of the device, with the result that light extraction efficiency is lowered.
For improving the light extraction efficiency, there have been proposed a number of methods of changing a traveling direction of light to break the total reflection condition, such as a method of providing fine uneven structure or lens structure on the surface on the light exit side so as to extract the propagating light out of the device. In particular, as a method having high improvement effects, there has been proposed a method of providing a transparent layer, the refractive index of which is equal to or higher than that of an emission layer, adjacently to a light exit side of a transparent electrode, and further providing a region for causing disturbance in reflection/scattering angles of light on the light exit side of the transparent layer or in the transparent layer (Japanese Patent Application Laid-Open No. 2004-296429).
According to the above-mentioned method, based on the classical Snell's law, propagating light in the emission layer which occupies about 80% of the light emitted by the emission layer is pulled in a high-refractive-index transparent layer whose refractive index is higher than that of the emission layer to be converted into propagating light in the transparent layer. The propagating light thus obtained is extracted out of the device through the region for causing disturbance in reflection/scattering angles of light on the surface of the transparent layer or in the transparent layer.
However, when the method of causing light to propagate through the high-refractive-index transparent layer is applied to a display apparatus such as a display, a peculiar problem occurs. Light which is guided to the high-refractive-index transparent layer and is finally output to the air through the region for causing disturbance in reflection/scattering angles of light includes light traveling at an angle equal to or higher than a critical angle, which is originally supposed to be totally reflected. This light is recognized as light emitted from a position different from an actual light-emitting point due to parallax caused by the thickness of the high-refractive-index transparent layer, and hence, there arises a problem of blur in a displayed image. In order to solve this problem, there has been proposed a method of adjusting the thickness of a substrate (although not the high-refractive-index transparent layer), through which light propagates, to a predetermined proportion or less of a pixel size (Japanese Patent Application Laid-Open No. 2005-322490).
Further, when the light guided to the high-refractive-index transparent layer enters the region for causing disturbance in reflection/scattering angles, the light is not necessarily extracted to an air side through one incidence. Light whose traveling direction has been changed by the region for causing disturbance in reflection/scattering angles is also totally reflected again to propagate through the high-refractive-index transparent layer in the case where the light travels at an angle equal to or larger than a critical angle in an interface between the high-refractive-index transparent layer and the air. Consequently, the light propagates laterally through the high-refractive-index transparent layer and is eventually output to the air side at a position away from the light-emitting point at which the total reflection condition has been broken. Therefore, there still arises a problem of blur in a displayed image. In particular, as the refractive index of the transparent layer is higher, the amount of high-angle component light is larger, and hence, the number of times at which the light enters the region for causing disturbance in reflection/scattering angles decreases, and the waveguide length in the lateral direction up to the point where the light is extracted to the air side increases, which renders the problem more serious.